I understood you, however there was a little confusion in your question. I also was answering this based on the availability of information in iOS 15. I had an older iPhone 7 that I had to charge up so I could make some comparisons with my iPhone 13 Pro and iOS 15.0.2.
It would appear that the ability to make some additional settings changes to Maps is no longer available. I don't use my vehicle for audio, as I get information from my Watch when using the iPhone for navigation. While I was able to test audio with both devices in my vehicle, I could not locate the ability to choose between the phone and the vehicle, as was present in the iPhone 7 with iOS 12.3.1.
At this point, you can use the Get Support link at the top of the page here to contact Apple Support with your query. Or, you can use the feedback link to report the information to Apple, but that will not get you an individual response. The feedback link is iPhone - Apple
As far as why Apple would bury a setting, no one here would know, and speculation about Apple decisions on this forum is prohibited by the terms of use.